Generally a minute portion of the air confined in the assembly of the tire and the rim is naturally leaking out as the time elapses.
When the air pressure of a tire is lower than the proper air pressure, steering, braking, and driving performance of a vehicle will be degraded.
In order to maintain the preset air pressure of a tire, the tire pressure detection system of the prior art measures the pressure or the temperature inside the tire using the tire pressure detection sensor mounted in the wheel and transmits this information to the control unit via the wireless communication.
However, the tire pressure detection system of the prior art simply alarm the driver when the tire pressure drops below the predetermined pressure, therefore, there has been a problem that still there is a risk of driving accident during driving to a vehicle service station, and intervening of the driver is necessary.
Further progressed from tire pressure monitoring system (TPMS), the necessity of development of an active tire safety device not requiring involvement of a driver when the tire pressure is decreased has been suggested.
Followings are the descriptions about a prior art related to tires capable of self-maintaining air pressure thereof.
(1) First, European Patent No. 1648721 (hereinafter refer to as ‘Prior Art 1’) is characterized in that a tube is installed between the tire and a rim flange 1a, and a valve and a filter are installed at the both ends of the tube.
Generally, the tube supplying air into the tire is made of a flexible material such as a rubber which is a softer material compared to the rim flange 1a made of a metallic material.
Thus, a problem exists in Prior Art 1 that the durability of the tube can be degraded as the tube is being contacted to the rim flange 1a continuously.
In addition, since the bead portion which is in the vicinity of the rim flange is unlikely to be deformed, there is a disadvantage that the compression and expansion of the tube supplying air into the tire are not performed smoothly.
However, compression of the tube may occur through the contact with the wheel, that is the rim flange, but in this case, disadvantages have been suggested that the durability of the tube is degraded including the problem as described above.
(2) U.S. Pat. No. 8,042,586 (hereinafter refer to as ‘Prior Art 2’) is characterized in that the bending region within a rolling tire footprint having a neutral axis, a compression sidewall, and an elongation sidewall, and a groove wherein the tube is installed is positioned within the compression sidewall, and a tube is positioned within the tube in contacting engagement with opposite groove surface.
Especially, in the case of Prior Art 2, it has been exemplary shown that the positions of the tube in the compression sidewall, wherein the compression of the tube is occurring during the rolling of the tire, are 200 in the outer surface, 202 in the inner surface, and 204 in the outer surface in FIG. 9B of Prior Art 2.
Prior Art 2 is characterized by suggesting a technology wherein the air is forced by the compression of the tube during the rolling of the tire.
However, actually the movement of a tire is accomplished by the up-down movement of folding and unfolding thereof due to the compression at the surface of contact with the road surface, that is, an active extension and contraction movement.
Therefore, it is desirable to position the tube in a place where the most active extension and contraction movement is occurring in order to inject the air into the tire cavity.
In addition, the device for maintaining a proper air pressure of a tire should be made to be as light as possible, since the weight of a vehicle is closely related to the vehicle's performance.
(3) In U.S. Pat. No. 8,113,254 (hereinafter refer to as ‘Prior Art 3’), a circular type air tube is connected to the inlet and outlet devices which have the shape of a letter “T.”
It is characterized in that the inlet and outlet devices are positioned facing each other.
In the case of Prior Art 3, there are disadvantages as follows.
First, the inlet and the outlet are facing each other with 180 degree symmetry, that is, only half of the total length of the tube is used, therefore the performance is relatively lower when compared to the method having the inlet and outlet devices located in same position, and moreover, there is a difficulty in installing when compared to the technology comprising only one device for installing.
Besides, the external air is constantly introduced into the tube since no regulator is formed in the inlet device, and the process of exhausting the air via the outlet device is repeatedly performed even at the preset air pressure.
Therefore, since the inlet and outlet devices of the tire must be operating continuously during the operation of the tire, this may cause a big problem of degradation in the durability of the inlet and outlet devices.
Moreover, there is a disadvantage that the manufacturing and setting method for the valve comprising the combination of two balls and respective springs is difficult when compared to the piston method having one spring.
U.S. Pat. No. 9,205,714 (hereinafter refer to as ‘Prior Art 4’) has an advantageous structure capable of minimizing the height using a regulator utilizing the thin layer of a membrane method.
However, in the case of Prior Art 4, it not only uses two check valves in order to prevent reverse flow of the air, but also uses a separate spring for the design of the regulator considering the high pressure of the tire, therefore, the structure becomes rather complicated and there is a difficulty in miniaturization thereof.
And, a fine adjustment for setting the preset tire pressure becomes impossible.
Moreover, disadvantages have been suggested that since the connection between the compression tube and the inlet and outlet port is accomplished inside the bead portion of the tire, it is too difficult to apply to the actual tire.
In U.S. Pat. No. 8,573,270 (hereinafter refer to as ‘Prior Art 5’), the introduction of the air is controlled by the disc-like pressure membrane made of a flexible material, and it is about a technology for miniaturization of the valve (or regulator).
Although the objective of miniaturization of the valve (or regulator) can be partially achieved by Prior Art 5, the pressure membrane is continuously receiving the centrifugal force along the radial direction when the tire is rotating.
Therefore, while there is an advantage of miniaturization of the valve (or regulator), the problem of degradation in the durability of the pressure membrane has been suggested.